1. Field of Invention
The present invention relates to a light source device, and an illuminating optical system and a projector including the light source device.
2. Description of Related Art
In projectors, light emitted from an illuminating optical system is modulated according to image information with the use of a modulation device such as a liquid crystal light valve, and the modulated light is projected onto a screen, thereby achieving image display.
In such projectors, in order to obtain a uniform in-plane distribution of illumination light for illuminating the modulation device, integrator illuminating optical systems for dividing light emitted from a light source lamp into a plurality of partial light beams and superimposing the partial light beams near the modulation device are used. Of such integrator illuminating optical systems, an integrator illuminating optical system (uniform illuminating optical system) using a light source lamp provided with an elliptical reflector, and a lens array, in order to collimate light emitted from the elliptical reflector to be input into the lens array, a spherical concave lens is commonly provided between the light source lamp and the lens array. That is, a light source device for emitting parallel light is formed by a combination of the light source lamp and the spherical concave lens.
However, the light beam emitted from such a light source lamp has high parallelism at the center, but has poor parallelism at the periphery thereof. This is caused by spherical aberration generated in the concave lens. In the illuminating optical system, or in a projector using the illuminating optical system, light beams with poor parallelism cannot pass through the lens array smoothly, and are often wasted. For this reason, according to a conventional illuminating optical system, it is difficult to efficiently utilize the light emitted from the light source lamp. This invention is made to solve the above-described problems in the conventional art, and an object is to provide a technique for increasing parallelism of light emitted from a light source device.
In order to solve at least a part of the above-described problems, according to the present invention, there is provided a light source device including:
a discharge lamp;
an elliptical reflector including a reflecting surface for reflecting light emitted from the discharge lamp; and
a lens for collimating the light reflected by the reflecting surface, the lens is an aspherical lens having an aspheric surface in the shape of a quadric surface of revolution on one of an incidence surface and an emission surface.
Since the light source device of the present invention includes the aspherical lens having an aspheric surface in the shape of a quadric surface of revolution on one of the incidence surface and the emission surface, it is possible to increase parallelism of light to be emitted.
In the above light source device, the aspheric surface may, for example, have the shape represented by the following expression when taking coordinate values in the rxcex8Z cylindrical coordinate system, in which the origin is the point of intersection of the aspheric surface and a light source optical axis and which is axisymmetric with respect to the optical axis, as r and Z, the paraxial curvature as c, and the conic constant as K:       Z    -                  c        ·                  r          2                            1        +                              1            -                                          (                                  1                  +                  K                                )                            ·                              c                2                            ·                              r                2                                                          =  0.
This can easily determine the shape of the aspheric surface. In addition, if the lens having the aspheric surface determined on the basis of the expression is used, spherical aberration can be greatly reduced. Therefore, the parallelism of light emitted from the light source device can be considerably increased.
In the above light source device, the aspheric surface may, for example, be a concave surface. In this case, since the lens can be disposed between a first focal point and a second focal point of the elliptical reflector, it is possible to reduce the light source device""s size.
In this case, the aspherical lens may be bonded to an opening surface of the elliptical reflector. This can further reduce the light source device""s size, and it is possible to allow the aspherical lens to function in front of the light source device.
In the above light source device, however, the aspheric surface may be a convex surface.
In the above light source device, the aspheric surface of the lens may, for example, be a concave surface or a convex surface, and the aspheric surface may, for example, have the shape of an ellipsoidal surface of revolution when the emission surface is an aspheric surface.
When the emission surface is an aspheric surface, the diameter of an emitted light beam can be reduced. Therefore, in a case where the light source device is used in an illuminating optical system or a projector, since the sizes of the optical elements disposed toward the downstream from the light source device can be reduced, the illuminating optical system or the projector can be reduced in size. Furthermore, when the emission surface is an aspheric surface, variations in an in-plane illuminance of the emitted light beam can be greatly reduced.
In this case, the ellipsoid of revolution may, for example, have the shape represented by the following expression in the rxcex8Z cylindrical coordinate system, in which the origin is the point of intersection of the aspheric surface and a light source optical axis, the light source optical axis is the Z-axis, and the axis perpendicularly intersecting the light source optical axis is the r-axis, as r and Z, the paraxial curvature as c, and the conic constant as K:             Z      -                        c          ·                      r            2                                    1          +                                    1              -                                                (                                      1                    +                    K                                    )                                ·                                  c                  2                                ·                                  r                  2                                                                          =    0    ,      xe2x80x83    ⁢  and
wherein the elliptical reflector may, for example, have the shape represented by the following expression in the rxcex8Z cylindrical coordinate system, in which the origin is the point of intersection of the reflecting surface and the light source optical axis, the light source optical axis is the Z-axis, and the axis perpendicularly intersecting the light source optical axis is the r-axis, as rR and ZR, the paraxial curvature as cR, and the conic constant as KR:                     Z        R            -                                    c            R                    ·                      r            R            2                                    1          +                                                    1                -                                  (                                      1                    +                                          K                      R                                                        )                                                      ·                          c              R              2                        ·                          r              R              2                                            =    0    ,
and KR is within the range of xe2x88x920.8 less than KR less than xe2x88x920.5.
This can easily determine the shape of the ellipsoid of revolution. In addition, if the lens having the aspheric surface determined on the basis of the expression is used, spherical aberration can be greatly reduced. Therefore, the parallelism of light emitted from the light source device can be considerably increased.
In the above light source device, the aspheric surface of the lens may, for example, be a concave surface or a convex surface, and the incidence surface of the lens may, for example, be a spherical surface when the emission surface is an ellipsoid of revolution.
This can prevent light from being refracted at the incidence surface of the lens and therefore, it is possible to obtain an emitted light of higher parallelism. When the incidence surface is a plane surface, the parallelism of the emitted light is less than a case where the incidence surface is a spherical surface. However, by forming one side of the aspherical lens into a plane surface, the aspherical lens can be produced at relatively low cost.
In addition, the ellipsoid of revolution, in which the aspheric surface of the lens is a concave surface or a convex surface, the emission surface is an ellipsoid of revolution, and the incidence surface is a spherical surface, may, for example, have the shape represented by the following expression in the rxcex8Z cylindrical coordinate system, in which the origin is the point of intersection of the aspheric surface and a light source optical axis, the light source optical axis is the Z-axis, and the axis perpendicularly intersecting the light source optical axis is the r-axis, as r and Z, the paraxial curvature as c, the conic constant as K, and the refraction index of the lens as n:             Z      -                        c          ·                      r            2                                    1          +                                    1              -                                                (                                      1                    +                    K                                    )                                ·                                  c                  2                                ·                                  r                  2                                                                          =    0    ,      xe2x80x83    ⁢      K    =          -                        1                      n            2                          .            
This can easily determine the shape of the ellipsoid of revolution.
In this light source device, the incidence surface of the aspherical lens may, for example, be formed with an ultraviolet reflecting film. This can prevent ultraviolet light from being emitted from the light source device. In addition, the ultraviolet light emitted from the discharge lamp is reflected back to the discharge light whereby intensity of visible light emitted from the light source device can be increased.
In the above light source device, the aspheric surface of the lens may, for example, be a concave surface or a convex surface, and the aspheric surface may, for example, have the shape of a hyperboloid of revolution when the incidence surface is an aspheric surface.
When the incidence surface is an aspheric surface, light reflected by the reflecting surface of the elliptical reflector is collimated by the incidence surface of the lens, and can be prevented from being refracted at the emission surface. Therefore, it is possible to obtain an emitted light of greater parallelism.
In this case, the hyperboloid of revolution may preferably have the shape represented by the following expression in the rxcex8Z cylindrical coordinate system, in which the origin is the point of intersection of the aspheric surface and a light source optical axis, the light source optical axis is the Z-axis, and the axis perpendicularly intersecting the light source optical axis is the r-axis, as r and Z, the paraxial curvature as c, the conic constant as K, and the refraction index of the lens as n:             Z      -                        c          ·                      r            2                                    1          +                                    1              -                                                (                                      1                    +                    K                                    )                                ·                                  c                  2                                ·                                  r                  2                                                                          =    0    ,      xe2x80x83    ⁢      K    =          -                        n          2                .            
This makes it possible to easily determine the shape of the hyperboloid of revolution. In addition, if the lens having the aspheric surface determined on the basis of the expression is used, spherical aberration can be reduced very small. Therefore, the parallelism of light emitted from the light source device can be considerably increased.
In this light source device, the emission surface of the aspherical lens may be a plane surface, and the emission surface of the aspherical lens may be formed with an ultraviolet reflecting film.
This can prevent ultraviolet light from being emitted from the light source device. In addition, the ultraviolet light emitted from the discharge lamp is reflected back to the discharge light whereby intensity of visible light emitted from the light source device can be increased.
It is possible to use the above-described light source device as a light source device in an illuminating optical system including a lens array for dividing light emitted from the light source device into a plurality of partial light beams, and a superimposing lens for superimposing the partial light beams divided by the lens array on an illumination area.
In addition, in the illuminating optical system, when a light source device is used in which an incidence surface of an aspherical lens has the shape of a hyperboloid of revolution and an emission surface is a plane surface, the lens array may be provided on the emission surface of the aspherical lens. This makes it possible to reduce the illuminating optical system in size.
In addition, it is possible to use the above-described light source device as a light source device in a projector including an electro-optical device having a light incidence surface as an illumination area illuminated by the light source device, and modulating the incident light from the light source device according to image information, and a projection optical system for projecting light modulated by the electro-optical device.
By using the above-described light source device as a light source of the illuminating optical system or a projector, it is possible to increase light utilization efficiency and increase the brightness of a projected image.